1. Field of the Invention
The present invention relates to an arrangement for calibrating probes such as AFM probes.
The present invention further relates to an atomic force microscope including such an arrangement.
The present invention further relates to a batch calibration device for calibrating a batch of probes, such as a batch of AFM-probes.
The present invention further relates to a method for calibrating AFM probes.
2. Related Art
Atomic force microscopes AFMs are widely used for the physical characterization of materials and devices when high spatial resolution and small feature sizes are of interest. AFMs are primarily used in imaging modes to provide topographic information, but they can also record the force interaction between the cantilever sensor tip and a sample.
Measuring the force interaction between the tip and surface involves measuring the deflection of a spring suspension. In the case of an AFM, the force sensor itself is a microfabricated cantilever that functions as a passive mechanical sensor. Users interested in small force measurements must therefore determine the suspension spring constant, or otherwise calibrate this deflection as a force.
Process non-uniformities and variations during fabrication of the cantilever, contaminations and imperfections lead to uncertainties in cantilever's spring constant. Therefore, a calibration of the AFMC is essential to enable reliable measurements. Similar probes are used in other instruments, such as indentation machines. Various calibration methods are known. For example FR 2887986 A1 discloses a method that involves placing an oscillator e.g. lever, in contact with a deformable object, where the oscillator has a resonance frequency, a mass and a stiffness. The oscillator is oscillated at its resonance frequency. A resonance frequency of the oscillator contacting the object is measured by determining a resonance curve of the oscillator by a synchronous detection, or by measuring an instantaneous resonance frequency of the oscillator between a position of non-contact of the oscillator with the object and a position of contact of the oscillator with the object. Another method is disclosed in SCHOLL D ET AL: “In Situ Force Calibration of High Force Constant Atomic Force Microscope Cantilevers”, REVIEW OF SCIENTIFIC INSTRUMENTS, AlP, MELVILLE, NY, US, vol. 65, no. 7, 1 Jul. 1994 (19940701), pages 2255-2257
A further method is disclosed in AKIHIRO TORII ET AL: “A method for determining the spring constant of cantilevers for atomic force microscopy”, MEASUREMENT SCIENCE AND TECHNOLOGY, BRISTOL, GB, vol. 7, no. 2, 1 Feb. 1996 (1996-02-01), pages 179-184. Therein the spring constant of an atomic force microscope (AFM) cantilever is measured by using a calibration lever formed by a large-scale cantilever. The spring constant of the AFM cantilever is determined by varying a displacement of a stage carrying large-scale cantilever and measuring the deflections of both cantilevers simultaneously using heterodyne interferometry. The spring constant of the AFM cantilever is determined from the slope of the measured deflection as a function of the stage displacement. The calibration lever is a large-scale cantilever, i.e. in the order of a centimeter long. The spring constant of the large-scale cantilever is determined by measuring both its deflection and the mass of a weight attached at the end of the large-scale cantilever. However, due to the large scale of the calibration lever the range in which the spring constant can be reliably measured is limited.